1. Field of The Invention
The present invention relates generally to devices and methods for silencing engines and, more particularly, to silencers for engines used in a marine environment that employ water cooling of the exhaust gas.
1. Related Art
One technique for silencing engines, particularly those used in a marine environment, is to add water (usually the engine cooling water) to the engine's exhaust gas. Typical applications are marine propulsion engines and electric generators for use in a marine environment. Discharge of the resulting mixture of exhaust gas and water is straightforward in applications in which the engine is situated above the waterline. In these cases, the water and gas mixture may simply be downwardly directed through a pipe for discharge through the vessel's hull. The downward angling of the pipe is provided so that water does not flow back through the pipe and into the engine.
However, in some applications the engine is located below the waterline, such as in some sailboats or displacement power boats. In those applications in which water is not mixed with the exhaust gas, and thus the cooling and silencing benefits of mixing with water are foregone, the hot gas may simply be directed upward and discharged above the waterline. Typically, before discharge, the hot gas is silenced by a device that may be similar to an automotive muffler. In those applications in which water is mixed with the exhaust gas at the engine, the resulting mixture must be lifted above the waterline and then directed downward for discharge through the hull. The vertical distance that the mixture must be lifted may vary between a few inches to ten feet or more.
A device commonly referred to as a "waterlift silencer" has been developed to cool and silence the exhaust gas and to lift the mixture of exhaust gas and water above the waterline. In a waterlift silencer, the mixture is introduced into a chamber (or series of chambers). The expansion of the mixture into the volume of the chamber reduces the acoustic energy of the exhaust. An exit tube conventionally is provided through which the mixture is expelled from the chamber.
One such conventional waterlift silencer is described in U.S. Pat. No. 3,296,997 to Hoiby, et. al. In the Hoiby device, the mixture of cooling water and exhaust gas is introduced into a chamber through an inlet pipe. An exit tube extends vertically through the top of the chamber. The bottom of the exit tube is spaced from the bottom of the chamber so that the mixture may enter the bottom of the tube and be expelled. As described by Hoiby, the gas separates from the water in the chamber and, when the dynamic pressure in the chamber is such as to depress the water level to the bottom of the tube, the gas escapes in a high velocity flow through the bottom of the tube and out of the chamber. The kinetic energy of the gas escaping through the tube partially atomizes the water, according to Hoiby, and entrains the atomized liquid particles. The entrained liquid is thus carried, along with the exhaust gas, up through the exit tube. A similar design is shown in U.S. Pat. No. 5,554,058 to LeQuire.
U.S. Pat. No. 2,360,429 to Leadbetter is one type of silencer that uses water to silence exhaust gas and includes multiple chambers. Other designs of marine silencers employing water silencing using multiple chambers are described in U.S. Pat. No. 5,147,232 to Miles, et al. (including a list of patents related to silencers for marine engines; see column 1). In the silencers described in Miles, multiple intermediate exhaust tubes are provided for carrying exhaust gas between chambers, and multiple outlet exhaust passageways are provided for expelling exhaust gas from the silencer. The silencer described in U.S. Pat. No. 2,498,979 to Bourne also shows multiple chambers and multiple pipes for expelling exhaust gas.